AT&T 518-600-016 manual Mu-Law

Mu-Law 255

Mu-Law 255 is a commanding scheme which uses a compression ratio that is compatible with modern channel bank equipment. The scale is divided into 16 intervals, with each interval having 16 levels. Therefore, it has 256 discrete values. Mu-Law 255 has a negative and positive zero; therefore, it really has 255 discrete values. This commanding scheme is used in the United States and Japan.

A-Law 100

The commanding scheme used in Europe is A-Law. It follows the same basic theory as Mu-Law 255 except that its scale is different. The scale tends to be more linear than Mu-Law 255. Because the intends tend to be equal, A- Law 100 does not concentrate its accuracy in areas of the scale where voice signals occur the most.

DIGITAL SWITCHING The Time Division Multiplex (TDM) bus allows many users to communicate over a common electrical connection. The TDM bus is physically distributed across the backplane of the control unit and connects all line/station modules. It is 8 bits wide and has a frequency of 2.048 MHz. The frame repetition rate is 8 KHz providing a 64 Kbps channel on each of the 256 time slots. The TDM bus has specific time slots for various functions. During a conversation between station A and station B, a time slot is reserved for station A to transmit on and another for station B to receive on. Because the TDM bus cycles 8 thousand times per second, the conversation is continuous. The TDM bus carries tones and control signals to stations. Unlike other bus configurations, the stations on the TDM bus receive all transmissions. If a station is not assigned to any of the time slots, the TDM bus will ignore the data. Refer to Figure 1-10for an example of the TDM bus.

The Digital Switch Element (DSE) functions as a digital switch for voice and data. It also performs the operations for commanding schemes such as A-Law and Mu-Law.

1-42 Theory of Operation